world, and it was seldom reproduced in Russian architecture, most notably in the St. Peter's and Paul Cathedral in Petergof and in the Church of the Savior on Blood in St. Petersburg. 1566 Great Abatis Line The Great Abatis Line, or Bolshaya Zasechnaya Cherta in Russian, was the largest fortification line of the abatis type, built by the Grand Duchy of Moscow and later the Tsardom of Russia. Its purpose was to protect Russia from the raids of nomads of the Eastern European steppes, such as the Crimean Tatars. As a fortification construction stretching for hundreds kilometers, the Great Abatis Line is analogous to the Great Wall of China and the Roman limes. Most of its length consisted of abatis, which is a barrier built from felled trees arranged as a barricade. It was also fortified by ditches and earth mounds, palisades, watch towers and natural features like lakes and swamps. Stone and wooden kremlins of the towns were also included in the Great Abatis Line, as well as the smaller forts called ostrogs. The Great Abatis Line was built south of Moscow between the Bryansk woods and Meschera swamps starting from the 12th century, and was officially completed in 1566, exceeding 1000 km in length. 1586 Tsar Cannon The Tsar Cannon is an enormous cannon, commissioned in 1586 by Russian Tsar Feodor and cast by Andrey Chokhov. It is the largest bombard by caliber. The cannon weighs 39.312 metric tonnes and has a length of . Its bronze-cast barrel has a calibre of , and an external diameter of . Along with a new carriage, the 2 ton cannonballs surrounding the cannon were added in 1835 and are larger than the diameter of its barrel; in fact, it was originally designed to fire 800 kg stone grapeshot. The cannon is decorated with reliefs, including one depicting Tsar Feodor on a horse, hence the name of the cannon, though now the word Tsar is associated more with the supreme size of the weapon. Several copies of the cannon were made in the 21st century and installed in Donetsk and several Russian cities, while the original Tsar Cannon is in the Moscow Kremlin. 17th century Bochka roof The bochka roof or simply bochka (, barrel) is the type of roof in the traditional Russian architecture that has a form of half-cylinder with an elevated and sharpened upper part, resembling the sharpened